An audio codec is generally any combination of hardware and software components that converts audio signals between analog and digital domains for generation of digital audio content and playback of digital audio content, sometimes while compressing or decompressing digital audio data.
Digital audio content playback capabilities of portable devices have increasing demand. For example, cell phones, PDAs, mp3 players, laptop computers or other electronics gadgets are devices for which consumers seek digital audio playback functionalities. To operate audio codecs, a system clock that is a multiple of the audio data rate is often needed, although the master clock in a system can be unrelated to the audio data rate. Typical compressed digital audio bit rates can include, for example, 32, 96, 128, 160, 192, 224, 320 Kbits/s, or other intermediate values. However, digital content may be encoded at one of several standard data rates such as, 8 or 16 kHz (voice), 44.1 kHz (CD-ROM), or 48 kHz (High Fidelity) while operating with one of many different master clock rates such as 12 MHz (USB), 11.2896 (CD-ROM), 13 MHz (GSM phone), or other system clock frequencies.
Therefore, one typical solution employs analog phase locked loops (PLLs) to generate the clock rate utilized by the audio code or other parts of the system. Analog PLLs can be ideal solutions for audio codec applications when they can be implemented with lower jitter voltage controlled oscillators (VCOs). Digital PLLs have generally been undesirable for audio codec playback applications as clock jitter when processing audio signals is non-ideal and can limit, for example, dynamic performance and sound quality. However, an analog PLL based solution is oftentimes expensive and resource intensive (e.g., area and/or power consuming). The applicability of analog PLLs to implementing audio codecs in shrinking audio playback devices may be limited.